A new case of IgE lambda paraproteinaemia is described in which the immunoproliferative disorder was lympho-plasmacytoid, rather than myelomatous in type. The patient, an 81-year-old woman, lacked both organomegaly and bone lesions. The peripheral white blood count was 30 X 10(9)/l (43% lymphocytes and 37% lymphoplasmacytoid cells) and the bone marrow was heavily infiltrated with mononuclear cells with 50% lymphocytes and 50% lymphoplasmacytoid cells). Detailed immunological marker analysis of both peripheral blood and marrow showed an increased population of morphologically normal T cells, together with neoplastic population of B cells. The neoplastic cells were shown to re-express surface immunoglobulin after stripping with anti-E anti-serum, and to synthesis Ig in radio-incorporation experiments. The immunological characteristics of the neoplastic cells are considered in relation to B-cell maturation and it is shown that the immunological phenotype was of the intermediate type to be expected in association with a lympho-plasmacytoid proliferation.